The present invention relates to breathable and flushable compositions and porous films and articles therefrom and a process for making these films. More particularly, the present invention relates to composites comprising a polymer that is water-soluble or water-degradable and a filler. In one embodiment, the composition of the invention comprises a polymer of ethylene oxide and a filler such as calcium carbonate.
Disposable products have revolutionized modern lifestyle and are of great convenience to society. Such products generally are relatively inexpensive, sanitary and quick and easy to use. Disposal of such products, however, increasingly is a problem as landfills close and incineration contributes to urban smog and pollution. Consequently there is an urgent need for disposable products that can be disposed of without dumping or incineration. An ideal disposal alternative would be the use of municipal sewage treatment and private residential septic systems. Products suited for disposal in sewage systems that can be flushed down a conventional toilet are termed xe2x80x9cflushable.xe2x80x9d An essential feature of flushable products is that they must have sufficient strength for their intended use, yet lose structural integrity upon contact with water.
Numerous attempts have been made to produce flushable fibers, fabrics, films and adhesives that retain their integrity and wet strength in the presence of body waste fluids, yet can be disposed of via flushing in conventional toilets. One approach to producing a flushable product is to limit the size of the product so that it will readily pass through plumbing without causing obstructions or blockages. Such products have high wet strength and do not disintegrate during flushing. Examples of this type of product include wipes such as baby wipes. This approach to flushability suffers the disadvantage, however, of being restricted to small articles.
Another approach to producing a flushable product is to manufacture a product that is normally insoluble in water, but which disintegrates in the presence of alkaline or acidic aqueous solutions. The end user is provided with an alkaline or acidic material to add to the water in which the product is to be disposed. This approach permits disposal via normal plumbing systems of products substantially larger than wipes, but suffers from the disadvantage of requiring the user to perform the step of adding the dissolving chemical to the water. A further disadvantage is that the inadvertent or intentional disposal of such a product in a conventional toilet without the addition of the dissolving chemical can cause serious obstruction or blockage of the plumbing system. The latter disadvantage can, however, be overcome by incorporating the dissolving acid or alkali into the article but separate from the dissolvable material while in use. The dissolving chemical is only released upon contact with water during flushing.
Similarly, another approach to producing a flushable product, particularly wipes, consists of forming the product from a pH-sensitive gelled polymer, and storing the product in the presence of a separate acidic solution. When the wipe is placed in a large quantity of neutral pH water, it disintegrates as a result of the pH shift. A disadvantage of this pH shift approach to flushability is that some acidic polymers lose wet strength at slightly alkaline pH in the range of 7-8. Because the pH of urine may be as high as 8.5, these flushable materials are not well suited for use in, for example, diapers or incontinence pads.
Another approach to producing a flushable product is to form the product from material that is susceptible to attack by specific enzyme catalysis that breaks down the structural integrity of the material. In such a product the enzymes may be introduced into the disposal water separately. These systems suffer many of the same disadvantages as those described above for alkaline or acid treatable materials.
It has been proposed to dispose of these products in municipal and private sewage systems. Ideally, these products would be flushable and degradable in conventional sewage systems. The term xe2x80x9cflushablexe2x80x9d as used herein means that the article is suited for disposal in sewage systems by flushing down through a conventional toilet. Disposal by flushing provides the additional benefit of providing a simple, convenient and sanitary means of disposal. However, while capable of being flushed, these personal care products must also have sufficient strength during use to provide the desired function for which they were designed. Personal care products should be able to withstand the elevated temperature and humidity conditions encountered during use and storage. However, to be flushable, they should lose integrity upon contact with water in the toilet.
Additionally, many disposable articles do not take into account the comfort of the user. Many of these articles use thermoplastic polymers which do not have high water vapor transmission rates and therefore do not have good breathability. It is desirable that these personal care products be breathable in order avoid the build-up of perspiration and increase the level of comfort of the wearers of these products. By increasing the breathability of the films, the skin wellness of the user is also increased since water vapor can pass through the film and article away from the skin and not be trapped against the skin, causing possible rashes or other skin maladies. Therefore, a breathable material having mechanical integrity when dry yet readily disintegrates upon immersion in water is highly desirable.
Due to its unique interaction with water and body fluids, poly(ethylene oxide) (hereinafter PEO) is currently being considered as a component material in flushable products. PEO,
xe2x80x94(CH2CH2O)nxe2x80x94
is a commercially available water-soluble polymer that can be produced from the ring opening polymerization of the ethylene oxide, 
Because of its water-soluble properties, PEO is desirable for flushable applications. However, PEO films are not highly breathable, as needed for personal care products, and are difficult to process using conventional processing techniques.
Prior art references have attempted to overcome these difficulties. U.S. Pat. No. 4,902,553 to Huang et al. discloses disposable articles comprising a liquid impermeable, vapor permeable film comprising a crystallizable, stretched polyolefin-based film and a rattle-reducing additive which may be polyethylene oxide. However, the liquid impermeable, vapor permeable films of U.S. Pat. No. 4,902,553 require at least one nucleating agent which may be talc or calcium carbonate. The amounts of nucleating agent are limited to very small amounts, 0.05 to 5 percent by weight. These amounts of inorganic nucleating agent are insufficient to be defined as fillers. Further, stretching is required to generate porosity and hence breathability and subsequent leaching of the rattle-reducing agent is the result. Additionally, these polyolefin films are not water-degradable and are therefore not useful in flushable applications. In contrast, the films of the present invention are based on a water-soluble or water-degradable polymer and not non-water-soluble and non-water-degradable polyolefins. The films of the present invention do not require a nucleating agent or a crystallizable polyolefin. Additionally, the films of the present invention may incorporate larger amounts, greater than 5 weight percent, of various filler(s).
U.S. Pat. No. 3,895,155 discloses coated, transparent plastic articles. The transparent plastic may comprise poly(ethylene oxide). An inorganic, protective coating is applied as a separate layer over the transparent plastic article to improve surface hardness, increase stretch resistance, and facilitate non-fogging. The inorganic, protective coating may comprise various metal oxides. However, the coating forms a separate, discrete, glass-like layer from the transparent plastic article and the resulting coating and articles are not breathable or flushable.
U.S. Pat. Nos. 5,075,153, 5,244,714, and 5,672,424 to Malhotra et al. disclose multilayered or coated recording sheets designed for electrostatic printing processes. The recording sheets comprise a base sheet with an anti-static layer which may be made from poly(ethylene oxide). The recording sheets comprise an additional toner receiving layer which comprises inorganic oxides such as silicon dioxide, titanium dioxide, calcium carbonate, or the like. The poly(ethylene oxide) and inorganic oxides are contained in separate layers, the anti-static layer and the toner receiving layer respectively. Therefore, the recording sheets are not breathable or flushable.
U.S. Pat. No. 4,276,339 to Stoveken describes a laminated product comprising a paper layer and a foamed layer. Poly(ethylene oxide) is described as one of many possible components of an aqueous dispersion of latex from which the foamed layer is made. Fillers such as clay or silica are suggested as possible additions to the aqueous dispersion of latex in order to increase the solids content and density of this aqueous dispersion. The aqueous dispersion from which the foamed layer is made must be foamed to be breathable. The present invention is drawn to breathable films that are not foamed. Additionally, there is no disclosure that the laminated product disclosed in Stoveken is flushable.
Thus, currently available PEO films are not practical for breathable, flushable personal care applications. What is needed in the art, therefore, are porous, breathable, flushable films and articles which overcome the difficulties set forth above, and methods of producing these breathable, flushable films and articles.
The invention discloses composites comprising a water-soluble or water-degradable polymer and at least one filler. Films made from the compositions disclosed herein have increased porosity, thereby increasing the breathability and flushability of the films. The polymer component forms the matrix of the composite. Desirably, the water-soluble or water-degradable polymer is a polymer or copolymer of ethylene oxide. Desirably, the filler is selected from clays, calcium carbonate or mixtures thereof. When the selected filler is calcium carbonate, it is also possible to surface treat the calcium carbonate with a liquid organosilicone having a Hydrophilic-Lipophilic Balance (HLB) number ranging from about 6 to about 12. In one embodiment, the polymer is a poly(ethylene oxide) and the clay filler is from the smectite group. Desirable clay fillers include montmorillonites and bentonites, for example sodium montmorillonite. In another embodiment, polyethylene oxide is grafted with one or more polar vinyl monomers.
Key variables that effect the microstructure of the composites of the invention include: filler particle size distribution, surface activity of the filler which may be modified and molecular weight and selection of the polymer. Preferably, the filler particles have an average particle size of less than about 10 microns. More preferably, the filler particles have an average particle size of less than about 5 microns. Even more preferably, the filler particles have an average particle size of less than about 1 micron. Smaller particle sizes provide improved dispersion and processability.
The composites of the present invention possess unique, porous structures. Films comprising the composites of the invention have enhanced breathability and water dispersibility. Such composites and stretched films comprising such composites are especially useful for flushable applications and are useful for making flushable articles such as flushable diapers, feminine pads, pantiliners, and training pants.